Aircraft used for the transport of cargo usually have cargo doors at a side of the aircraft. A loader may load a unit load device (ULD) into the aircraft through one of the cargo doors. In an area in the vicinity of the door inside the aircraft, motorized devices in the floor of the cargo hold are able to pull the ULD into the aircraft and then direct it to the final storage and transportation location, where it may be locked in place. The ULD may be moved forwards or aft by motorized rollers, or power drive units (PDUs), in the floor.